Tonkinaphaenops impunctatus Faille & Huang, sp. nov.

(Figs. 1, 6–8, 14D)

Holotype. ♂; Vietnam: Cao B ằng province: Trà Lĩnh district, Qu ốc To ản commune, Bản Danh: Hang R ắn (snake cave) (=TH06); 22°46’42.3’’N 106°18’49.8’’E, 642m; coll. A. Faille, P.V. Phu, V.T. Tu; 17 October 2018; MNHN.

Paratypes. 1 ♂ and 1 ♀; same data as holotype; SMNS . 1 ♀; same data as holotype; MNHN . 1 ♀; same data as holotype; IEBR . 1 ♂ and 1 ♀; same data as holotype; SCAU . 1 ♂, same locality as holotype; 18 October 2018; MNHN . 1 ♂ and 1 ♀; spares in ethanol; same data as holotype; SMNS . 1 ♀, same locality as holotype, 18 October 2018; SMNS .

Description. Similar to T. yinquanicus . Habitus as in Fig. 6. Length: 5.6 mm (from the middle of the labrum to apex of the elytron). Body elongate, elytra wide and convex, amygdaloid. Narrow fore-body; elytra wider than pronotum, which is as wide as the head. EL: 3 mm, EW: 1.8 mm. PL: 1.3 mm, PW: 0.98 mm. HL: 1.05 mm, HW: 0.76 mm. AL: 3.95 mm. Color: body reddish brown, concolor, shiny. Fore body long and narrow, hind body elongated obovate, strongly convex dorsally. Posterior pronotal setae lacking. Pronotum covered with a small, sparse and short pubescence. Microsculpture: transverse meshes, very fine on elytra and pronotum, more visible and less transverse on the head.

Etymology. The specific epithet is an adjective referring to one of the main character differing from the other species of the genus, the absence of punctuate striae in the last fifth of the elytra.

Remarks. The new species is close to Tonkinaphaenops marinae (Fig. 2) and T. yinquanicus (Fig. 3) but differs from the first in the punctuation of elytra, which is effaced well before the end of the apex whereas the dots reach the apex of the elytra in T. marinae . It is also distinct by the shape of the male genitalia, whose apex is rounded and flattened, similar to the next described species, while it is hooked in T. marinae . From T. yinquanicus, it differs in the shape of male genitalia less rounded at apex and the position of the 3 rd pore of marginal umbilicate series closer to the 2 nd than to the 4 th whereas it is equidistant in T. yinquanicus . Furthermore, the species is clearly distinct from the other species of Tonkinaphaenops by the presence of a small, sparse and short pubescence on the pronotum (mainly visible in lateral view) and the lack of pronotal posterior seta.

Nevertheless, and because the only known specimen of T. marinae is immature with a genitalia weakly sclerotized, new exemplars of T. marinae from the type locality would be necessary to confirm the differences in the shape of male genitalia between the two species.

Distribution. Known only from the type locality (Fig. 1).

This cave is a tunnel, with a development of more than 800 m (R. Huttler pers. comm.), the main part of the cave is fossil and dry. The beetles were collected in the wettest part of the cave, running on the clay (Fig. 8).